1) Field of the Invention
The present invention relates to a disk drive apparatus and a servo control circuit that perform positioning of a head using servo information recorded on a recording medium, a method of manufacturing a recording medium, a magnetic recording medium, and a method of checking a recording medium, and more particularly, to a disk drive apparatus and a servo control circuit that can improve the quality of servo information used for servo control and can prevent performance degradation and follow-up control failure due to defective servo information, a method of manufacturing a recording medium for disk apparatuses, a magnetic recording medium, and a method of checking a recording medium.
2) Description of the Related Art
In recent years, mass storage volume of a magnetic disk apparatus used as a storage apparatus for computers or audio-visual (AV) equipment is advancing significantly. The mass storage volume is realized owing to increase in data recording density in a magnetic disk, and a recording density of servo information has also been increased along with the increase in data recording density in a magnetic disk.
The term “servo information” means information recorded on a magnetic disk of a magnetic disk apparatus in advance, and it is information read at fixed intervals by a magnetic head to be used for positioning the magnetic head.
While the servo information is written on a track of a magnetic disk at fixed intervals by the same element number as the number of sectors using an exclusive apparatus called “servo writer”, after the magnetic disk has been assembled in a magnetic disk apparatus, the time required for writing servo information is increased according to the increase in recording density of servo information. This results in reduction in productivity of the magnetic disk apparatus.
In view of these circumstances, a magnetic transfer technique that collectively records servo information on a magnetic disk using an apparatus called “a magnetic transfer apparatus” has been developed in order to solve the problem about increase in the time for writing servo information.
In the magnetic transfer, the time for writing servo information can be reduced by applying direct magnetization to a master medium recorded with servo information in advance and a slave medium to be written with the servo information that is brought in close contact with each other to perform collective transfer of the servo information (see, for example, Japanese Patent Application Laid-open No. H4-251440).
Furthermore, techniques for detecting transfer defects before and after magnetic transfer, such as a foreign material check for checking whether foreign material is on a slave medium or a read-write check for writing a signal on a slave medium and reading it therefrom, have been developed (see, for example, Japanese Patent Application Laid-open No. 2002-25054).
In the conventional magnetic transfer system, however, when there is any omission in servo information after being transferred, a sector corresponding to the servo information becomes unusable. Accordingly, there is a problem that performance degradation due to a skip processing to the unusable sector or the like, or follow-up control failure occurs.